1. Field of the Invention
The invention relates to an oscillating undercarriage for a drilling device. An oscillating undercarriage of such type has a chassis, two undercarriage units which are arranged laterally on the chassis and supported in a pivotable manner, two oscillating cylinders for pivoting the undercarriage units relative to the chassis, with an oscillating cylinder being assigned to each undercarriage unit, and hydraulic lines which are arranged on the oscillating cylinders for actuation of the oscillating cylinders, wherein the hydraulic lines are connected to one another for pivoting the undercarriage units in opposite directions.
2. Description of Related Art Including Information Disclosed Under 37 CFR §§1.97 and 37 CFR 1.98
Drilling devices used in specialist foundation construction, in quarry and/or mining are frequently required to operate on uneven ground and/or construction sites that have a low load-bearing capacity. To improve their cross-country mobility and climbing capacity these drilling devices are in most cases equipped with crawler-type undercarriages.
To further improve the cross-country mobility and/or to minimize punctiform highly surface pressures and therefore to reduce the risk of soil failure undercarriages are known, in which the two undercarriage units containing the crawler tracks are not connected in a rigid manner to each other but are able to make a nodding movement independently of each other about an axis extending horizontally and transversely to the driving direction of the undercarriage units. To this end the undercarriage units are pivotably supported about the axis on the chassis and, located at a certain distance to the axis, they have a respective point of articulation for a hydraulic cylinder, the cylinder being in turn articulated to the chassis on the side facing away from the undercarriage unit. In such an arrangement the operating forces and torques are transmitted in the form of a force couple from the chassis to the undercarriage units. Through an extension or shortening of a hydraulic cylinder the respective undercarriage unit can be brought into different angular positions with respect to the chassis.
The nodding movement resulting from the pivoting of the undercarriage units is most often referred to by the term “oscillation”. Accordingly, the corresponding undercarriage is referred to as the oscillating undercarriage, the axis about which a pivoting takes place is referred to as the oscillation axis and the hydraulic cylinders provided for generating the movement are referred to as the oscillating cylinders.
A crawler-mounted drill vehicle having an oscillating undercarriage is known for example from EP 0 332 883 A1.
As a rule, the two oscillating cylinders are connected to each other in such a manner that both the two piston-head chambers and the two ring surface chambers of the two oscillating cylinders are each connected to one another hydraulically. If, in such an arrangement, different surface pressures occur on the undercarriage units during driving on uneven ground, an automatic pressure balancing takes place in the respective mutually communicating cylinder chambers during movement of the undercarriage units. The resultant opposed movement is referred to as “passive” oscillation or “oscillation automatic”.
To broaden the functions of the oscillating undercarriage a conveyor device can be provided, by means of which two mutually connected chambers can be supplied simultaneously from the outside with oil, whereas in the chambers lying opposite oil is discharged. If piston surfaces of different dimensions are present on both sides of the cylinder pistons, the system is supplied as a whole with oil or oil is discharged from the system. In this, the movement carried out by the undercarriage is referred to as “active” oscillation. In the case of active oscillation the oscillating cylinders are operated in the same direction so that the chassis can be lowered or raised with regard to the two undercarriage units. This can be of particular advantage in loading operations and/or when driving on steep construction site ramps.
If, in the exceptional case, damage occurs at an oscillating undercarriage on the hydraulic lines, which can be ascribed for example to an external influence occurring during rough drilling operation, a sudden draining of the oscillating cylinders can take place which is accompanied by a sudden tilting of the entire chassis and, if applicable, together with a drill mast arranged thereon. Due to the potential danger involved here a state as such is to be avoided.
It is known to make use of ball valves in the supply lines of the oscillating cylinders. However, more often than not these valves cannot be closed quickly enough during driving when line breakage occurs, for which reason they cannot be employed for line breakage safety.
Furthermore, so-called hose or pipe breakage safety devices are known which, on being flow-activated, take effect on reaching a critical flow rate. However, such safety devices operate in a comparatively viscosity-dependent manner, i.e. in a temperature-dependent way, and under certain circumstances they can only take effect with an intolerable delay, so that these safety devices can at best be employed to a limited degree for the purpose of protecting an oscillating undercarriage against line breakage.
Moreover, during the movement of an oscillating undercarriage on terrain it is possible that in the exceptional case of a drilling device having an extreme off-center position of its centre of gravity, e.g. due to a drill mast positioned extremely off-center, the passive oscillating movement can lead to an even more unfavourable displacement of the center of gravity, which can in turn increase the surface pressure and accelerate the oscillating process. Hence, in the exceptional case the system can become unstable which in the extreme might lead to an overturning of the device.
In the connecting lines for the oscillating cylinders the provision of unblockable check valves is known, to which pressure is applied automatically during driving of the drilling device, which annuls the unblocking and permits an oscillation of the undercarriage units. Though, when the device is stationary the oscillation is prevented. However, with such a device an overturning during driving cannot be prevented without any means.